A number of orthoses have been designed to restore stance and walking in paraplegic subjects. Among them, the reciprocating gait orthosis (RGO) appears to be one which is most widely adopted. The great energetic cost of orthotically aided walking is the main factor limiting the walking capability of paraplegic subjects. The purpose of the present research was to give a complete biomechanical evaluation of RGO locomotion in order to provide data that can be used for further improvements of the orthosis. From the whole body kinematics the mechanical work done to move the orthosis was estimated; by measuring the actual metabolic cost of RGO locomotion the efficiency was evaluated as the ratio between mechanical work and energy expenditure. It is found that RGO locomotion is a very demanding task in terms both of energy expenditure and of the mechanical work required. Furthermore, it is evident that the major determinant of this poor efficiency of RGO locomotion is the enormous amount of work required to move the orthosis which, in turn, reflects its poor mechanical characteristics. To accomplish the demand of real mobility, devices for transferring work from the upper to the lower portion of the body must be substantially improved. This technical aspect must be parelleled by suitable training programmes especially designed to improve the aerobic power of paraplegic subjects and their body composition (ie less fat and more muscle).